In the continuous setting, we consider WZ-pairs with respect to \((D_x, D_y)\) , i.e., the
pairs of the form \((f, g)\)  with \(f, g\in K(x, y)\)  satisfying \(D_x(f)= D_y(g)\) .

A WZ-pair \((f, g)\)  with respect to \((D_x, D_y)\)  is called a log-derivative pair if there exists nonzero \(h\in K(x, y)\)  such that \(f = D_y(h)/h\) 
and \(g = D_x(h)/h\) .

The following theorem shows that any WZ-pair in the continuous case is a linear combination of exact and log-derivative pairs,
which was first proved by Christopher in [1]} and then extended to the multivariate case in [2]}, [3]}.
